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Technical Description of OBD-II Trouble Code
Heater Resistance of HO2S (Bank 2 Sensor 3)
What does that signify?
This diagnostic trouble code (DTC) is a generic powertrain code that is applicable to all vehicles manufactured from 1996 onwards (Chevrolet, Ford, GMC, Mazda, Pontiac, Isuzu, etc.). Although it is a generic code, the specific repair steps may vary depending on the make and model of the vehicle.
In my personal experience, a stored code P0061 indicates that the powertrain control module (PCM) has detected a malfunction in the heater circuit of the downstream oxygen (O2) sensor for engine bank one. Bank 2 specifies that the malfunction pertains to the bank of the engine that does not contain the number one cylinder. Sensor 3 indicates that the problem is associated with the downstream sensor.
A typical O2 sensor consists of a zirconium dioxide sensing element, which is protected by a vented steel housing. The sensing element is connected to wire leads in the O2 sensor wiring harness with platinum electrodes. The O2 sensor transmits data to the PCM via the controller area network (CAN). This data includes information about the percentage of oxygen particles in the engine exhaust compared to the oxygen content of the surrounding air. The PCM uses this data to calculate fuel delivery and ignition timing. During cold start conditions, the PCM uses battery voltage to preheat the O2 sensor. The O2 sensor signal circuits are accompanied by a circuit dedicated to preheating the sensor. The heater circuit typically consists of a battery voltage wire (minimum 12.6 volts) and a system ground wire. The PCM applies battery voltage to the O2 sensor heater when the engine coolant temperature is low. This usually continues until the PCM enters closed loop operation. Voltage is routed through the PCM, sometimes with the assistance of a relay and/or fuses. The circuit is activated when the ignition switch is turned on during cold start conditions. The PCM is programmed to deactivate the O2 heater circuit once the engine reaches normal operating temperature.
When the PCM detects a level of resistance in the O2 sensor heater circuit that exceeds the programmed limitations, it stores a code P0061 and may illuminate a malfunction indicator lamp (MIL). In certain vehicles, the MIL may only be illuminated after multiple ignition cycles with a failure. If this applies to your vehicle, you will need to use the OBD-II readiness mode to ensure the success of your repairs. After performing the repairs, drive the vehicle until the PCM either enters readiness mode or the code is reset.
Severity & Symptoms
A stored code P0061 should be considered severe because it indicates that the upstream O2 sensor heater is not functioning. Symptoms of this engine code may include:
Causes
Possible causes of a P0061 trouble code may include:
Possible Solutions
A good starting point is to check for technical service bulletins (TSB) specific to your vehicle. Your issue may be a known problem with a known solution provided by the manufacturer, which can save you time and money during diagnosis.
When attempting to diagnose a code P0061, it is recommended to have a diagnostic scanner, a digital volt ohmmeter (DVOM), and a reliable source of vehicle information, such as All Data DIY.
A visual inspection of system wiring harnesses and connectors is a logical first step. Pay close attention to harnesses that are located near hot exhaust pipes and manifolds, as well as those that are near sharp edges like those found on exhaust shields.
Next, use the DVOM to test all system fuses and fusible links. Skilled technicians would test these components under load, as fuses that are not loaded may appear to be operational but can fail when loaded. You can load this circuit effectively by activating the O2 sensor heater(s).
The next step is to retrieve all stored trouble codes and freeze frame data. This can be done by connecting the scanner to the vehicle diagnostic port. Write down this information as it may be helpful if the P0061 code proves to be intermittent. Clear the codes and test drive the vehicle to see if the P0061 is immediately reset.
When the engine is cool enough to activate the O2 sensor heater and the code is reset, observe the O2 sensor heater input data using the scanner data stream. Narrow down the data stream display to include only relevant data for a faster response. If the engine is within the correct temperature range, the O2 sensor heater voltage should be approximately the same as the battery voltage. If a resistance issue causes the O2 sensor heater voltage to deviate from the battery voltage, a P0061 code will be stored.
You can monitor live data from the O2 sensor heater circuit by connecting the DVOM test leads to the sensor ground and battery voltage signal wires. Test the O2 sensor resistance using the DVOM. Remember to disconnect all related controllers before testing the system circuit resistance with the DVOM.
Additional diagnostic tips & notes:
Professional Service
While we always recommend seeking professional mechanical assistance to resolve this issue, if for some reason that is not possible, we offer the option to permanently delete this specific DTC. All other codes will continue to function normally. If you are interested in this option, please upload your ECU file to our portal.
